HLA typing was performed on lymphocytes from patients with a common disease or from families where more than one individual had a common disease type. HLA typing was performed in a cohort of individuals with AIDS, either Kaposi's sarcoma, or opportunistic infections, or individuals at risk for this disease. A total of 250 individuals have been HLA typed. One hundred of these patients have been followed over a 4-5 year period. The objectives of these studies are to examine possible genetic susceptibility to the development of AIDS or AIDS-related complex that is related to expression of histocompatibility antigens. The HLA-DR1 phenotype is increased in frequency in all AIDS patients compared to HIV sero-positive controls. HLA- DR3 is significantly decreased in the patients with Kaposi's sarcoma. In the HIV seropositive individuals followed for 54 months, 22 have developed AIDS (opportunistic infection). These individuals have a significant increase in the HLA-DR1 and/or DR3 phenotype. HLA-DR antigen frequencies increase in the HLA-DR1 and/or DR3 phenotype. HLA-DR antigen frequencies were compared with antibody production to DNA and RNA antigens in patients with systemic lupus erythematosus. Individuals with the HLA-DR3 and DR4 phenotypes were found to have antibodies to different nucleic acids.